The National Weather Service on Wednesday night was forecasting heavy rain, strong wind gusts and coastal flooding for southern Maine, but said the brunt of the storm would occur when most of us are asleep.

Wind gusts early Thursday were expected to reach 50 mph and rainfall to total 2 to 3 inches, said James Brown, a meteorologist with the weather service’s Gray office.

The worst conditions were expected around 12:37 a.m., when Portland was to have an astronomical high tide of 10.9 feet. The tide, whipped by strong winds, could cause flooding on the city’s waterfront, the weather service warned.

The storm, which is expected to end around midmorning Thursday, will bring unusually high temperatures for this time of year. Brown said the temperature in Portland could reach 70 degrees, much higher than the seasonal norm of 55 degrees.

Brown said the area could get another round of rain and possibly thunderstorms late Thursday afternoon or early evening.

Earlier Wednesday, Portland officials warned residents that astronomical high tides combined with heavy rains produced by the remains of Hurricane Patricia could combine to flood some downtown streets.

Wednesday’s forecast suggested the flooding wouldn’t be as severe as it was Sept. 30, when some city streets were waist deep in water and dozens of cars were trapped by floodwaters. But city officials encouraged residents to avoid parking in flood-prone areas during the high tides Wednesday night and Thursday afternoon.

“Extreme rain events can cause street flooding in many parts of the city when stormwater and sewer systems are stressed over their capacity,” said the city alert. “When such events occur during higher than normal tides, flooding may become significantly higher.”

City crews planned to monitor conditions Wednesday night, and barricade streets if necessary, the alert said.

The areas of Portland that have often flooded include the Bayside neighborhood along Somerset Street; East Bayside on Marginal Way east of Boyd Street; Park Avenue near Interstate 295; and the Portland waterfront on Portland Pier and parts of Commercial Street.

Tom Hawley of the National Weather Service in Gray said as much as 3 inches of rain could fall at the headwaters of the Saco River, which could lead to minor flooding there.

In urban areas, flooding could be compounded by storm drains clogged with fallen leaves, he said.

“We do have a coastal flood watch in effect,” Hawley said. “The seas will be building due to increased wind speed over the water.” He said beach erosion was possible with high seas generating waves up to 10 feet, though by the Thursday afternoon high tide, winds are expected to shift from southeast, which is toward the coast, to southwest, which is parallel to much of it. The heaviest rain and strongest winds were expected between 10 p.m. and 6 a.m.

Portland’s alert includes these recommendations: Avoid driving or walking through ponded water, as sewer manhole covers can be displaced and roads and sidewalks can be damaged during flooding; never drive or walk around road closure barricades; avoid leaving cars parked for long periods in the areas prone to flooding, keep an eye on rain conditions and be aware of higher than usual tides.

The weather service issued a coastal flood advisory effective until 3 a.m. Thursday. A wind advisory will remain in effect through 9 a.m. Thursday.

David Hench can be contacted at 791-6327 or at:

dhench@pressherald.com